1. Field of the Invention
This invention relates generally to flexible shaft couplings having intermeshing gear teeth and more particularly to continuously lubricated gear type couplings connected to shafts by keys and means to prevent air or corrosive gases from entering the interior of the coupling through the space occupied by the key.
2. Description of the Prior Art
Conventional prior art continuously lubricated gear type couplings include a pair of coupling halves each having a hub which has outwardly extending gear teeth and a sleeve surrounding each hub and having inwardly extending gear teeth in meshing engagement with the gear teeth of the hubs. Each hub is secured to the end of a shaft by a key inserted in keyways formed in the hubs and in the shafts. The shafts are substantially co-axially aligned and each coupling half is rotatably connected to each shaft. A spacer is connected between each of the coupling halves thus allowing the transmission of torque from one shaft to the other shaft. Each end of the spacer which is connected to each of the coupling halves contains a circumferentially extending trough. The spacer further includes a plurality of openings that extend from the trough through the spacer and into the upper portion of each coupling half. At the opposite end of each of the coupling halves, each sleeve contains a plurality of openings extending from the interior of the coupling near the intermeshing gear teeth to the outside of each of the coupling halves. A lubricant is continuously supplied to the trough at each end of the spacer and, as the coupling rotates, the lubricant flows through the openings into the interior of each coupling half. As the coupling rotates, the centrifugal force keeps the lubricant in contact with the inside surface of each of the sleeves. The lubricant flows along the inside surface of the sleeve to the intermeshing gear teeth thus lubricating the gear teeth so damage to the gear teeth does not result from metal to metal contact. The lubricant flows through the spaces between the intermeshing gear teeth and out through the openings at the end of each coupling sleeve. An example of one type of continuously lubricated coupling is shown in Zrodowski U.S. Pat. No. 2,726,523.
Although the prior art couplings perform well in that they transmit a great amount of torque and maintain constant lubrication between the intermeshing gear teeth, they do have a number of disadvantages. Because the lubricant is introduced through the openings in the spacer near the inside surface of the sleeve and is directed to the intermeshing gear teeth by the centrifugal forces caused by the rotation of the coupling, the lubricant is prevented from reaching the interior portions of the coupling. In addition, because the lubricant flows through the openings in the spacer and out through the openings in the sleeves, it causes a slight vacuum in the interior portions of the coupling. This slight vacuum in the interior of the coupling causes air to flow from outside the coupling through the keyways formed in the hubs and shafts and into the interior of the coupling. It has been found that when a coupling is used in an environment that contains a corrosive gas such as hydrogen, the hydrogen flows through the keyways and into the interior of the coupling. The hydrogen or other corrosive gases attack the metal of each coupling half that is not protected by the lubricant. In particular, this corrosive gas corrodes the interior of the spacer between the coupling halves below the lubricant openings in the spacer and causes cracks to form in the spacer which causes the spacer to break prematurely.
The obvious way to prevent the introduction of corrosive gases into the interior of the coupling through the keyways is to eliminate the key as a means of rotationally securing each coupling half to each shaft. This can be accomplished by utilizing conventional keyless hydraulic fit connections. However, the use of such hydraulic connections is extremely expensive and such solutions to the above problem are not acceptable in many instances. Thus, other solutions must be found to prevent corrosive gases from entering the coupling when the coupling utilizes keys to secure each coupling hub to the shaft.